(a) Field of the Invention
The invention relates to a transflective liquid crystal display. More particularly, the invention relates to a transflective liquid crystal display that can improve reflectivity and transmittance, and prevent gray inversion in reflective and transmission modes during occurrence of a time difference in generation of external light.
(b) Description of the Related Art
A liquid crystal display as one of flat panel display devices that are widely used includes two display panels where field generating electrodes such as a pixel electrode and a common electrode are formed, and a liquid crystal layer interposed therebetween, and the liquid crystal display generates an electric field in the liquid crystal layer by voltages applied to the field generating electrodes to determine alignment of liquid crystal molecules of the liquid crystal layer and control polarization of incident light, thereby displaying an image.
Such a liquid crystal display is classified as a reflective liquid crystal display and a transmissive liquid crystal display according to a light source.
The transmissive liquid crystal display has a structure in which a panel maintains liquid crystals that function as electro-optical switches between a pair of substrates, a backlight is disposed as a light source at the back surface of the panel, and an image can be viewed from the front of the panel. The use of the backlight is essential in a backlit liquid crystal display, but the backlight consumes a large amount of power so that the transmissive liquid crystal display is inappropriate to be used as a display of a portable device.
The reflective liquid crystal display has a structure in which a reflective plate is disposed at a bottom surface of a panel and light entering from the front is used as reflective light so that an image can be viewed from the front. Unlike the transmissive liquid crystal display, the reflective liquid crystal display is appropriate to be used as a display of a portable device because it does not require a backlight supplying light from the bottom, and thus consumes less power. However, the reflective liquid crystal display has spatial and temporal limitations because the optical effect of the reflective liquid crystal depends on the peripheral environment.
In order to overcome the drawbacks of the reflective and transmissive liquid crystal displays, a transflective liquid crystal display has been proposed. The transflective liquid crystal display can assure excellent optical characteristics without spatial and temporal limitations so that it has been applied to a mobile display.
However, a technique for realizing a complex mode in a single cell gap and a technique for applying a dual cell gap to a single mode have complex process problems and one pixel is divided into a transmission area and a reflection area so that the aperture ratio may be decreased, thereby causing deterioration of optical characteristics of the display.
Thus, a transflective liquid crystal display that can realize a reflection mode using external light and a transmission mode using a backlight unit in one pixel instead of dividing the pixel into the transmission area and the reflection area has been activated studied.
However, such a transflective liquid crystal display includes two liquid crystal panels so that reflectivity and transmittance may be deteriorated, and a time difference may occur when external light passes through the two liquid crystal layers.
In addition, when such a transflective liquid crystal display is realized using one liquid crystal panel, external light enters when a black gray of a transmission mode is expressed, and in this case, the gray becomes a white gray in a reflection mode due to the external light so that a desired gray cannot be expressed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.